Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 272222
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
422 PM MDT Wed Mar 27 2024

.SYNOPSIS...High pressure will push east, with increasing clouds
and southwest winds ahead of a cold front Thursday. That front
will bring snow, primarily to the northern mountains. It will
stall further south and weaken. After showers much of Friday,
mountain snow is likely Saturday through Monday.

&&

.SHORT TERM (Through 12Z Friday)...A ridge axis is tracking across
southwest Wyoming and Utah. Clouds will increase through the
evening as the ridge pushes east with synoptic flow transitioning
to the southwest. An expansive longwave trough will dig into the
PacNW Thursday, with southwest flow increasing for Utah through
the morning. The strongest winds will be throughout southwest
Utah, for portions of Iron and Millard counties, where enhanced
southwest flow often exceeds model guidance. HREF 50th percentile
gusts, are generally from 45-50 mph there, peaking late in the
morning into the afternoon. A Wind Advisory is in effect for those
gusty winds. Winds will taper off by around 6 PM as a cold front
approaches. Gusty south to southwest winds are likely for the Salt
Lake and Tooele valleys, peaking during the morning.

A cold front will push into northwest Utah Thursday morning. With
strong cold advection with that boundary and strong warm air
advection ahead of it, frontogenesis with a strong frontal band
will likely occur. Different guidance is in good agreement on
that, with snowfall rates likely peaking at more than 1 inch per
hour. Timing of the frontal boundary and enhanced precipitation
rates will be from roughly 2-5 PM for the far northern mountains
and 4-6 PM for the Wasatch Mountains. Enhanced precipitation rates
could bring snow to benches, with lower probabilities for valley
snow. Mountain snow showers will last longer, but the highest
rates will be during the afternoon near the cold front. As the
cold front pushes further south, it will stall and weaken, with
isolated snow showers into Friday.

Snow accumulation of 5-10 inches is forecast for most of the
northern mountains, with locally higher totals in the upper
Cottonwoods. A Winter Weather Advisory is in effect for several
northern mountain zones for the forecast snow accumulation.

.LONG TERM (After 12Z Friday)...A potent upper-level low will
approach the northern California coast Friday, bringing continued
southwest flow aloft over the Great Basin along with weak
shortwave ridging. This slight change in the flow aloft combined
with Thursday`s shortwave washing out will cause the leftover mid-
level boundary over central/southern to stall out as a stationary
front and even retreat northward as a quasi warm front. Lingering
showers with this boundary will bring additional light snow
showers to the mountains from roughly Brian Head to the Uintas
Friday and a chance of valley rain showers, though with only light
accumulations and little to no impacts.

Focus then turns to the inland progression of the aforementioned
upper-level low and its effects on our area as a 120kt+ jet punches
into the southwest US. The deterministic GFS and GFS ensemble show a
decaying atmospheric river just brushing southwest Utah Saturday as
it curves cyclonically around the south end of the Sierra. Related,
WPC`s Excessive Rainfall Outlook shows a marginal risk of rainfall
exceeding flash flood guidance nosing into lower Washington County.
Regardless of whether the moisture tap reaches the technical
definition of an AR, the main message is that southern Utah
mountains, especially those favored in southerly flow, will see a
period of heavy snow Saturday into Sunday above about 7000 feet.
Inch/hour rates are more likely than not during this period, with
the main uncertainty at this point being timing. NBM probabilities
show about a quarter to half inch of liquid for valleys (25th-75
percentiles).

Meanwhile, though farther removed from the main moisture stream, the
rest of the forecast area will get it on the action as well with
plenty of upper-level forcing for ascent and yet another surface
boundary setting up along the central spine of Utah mountains. In
contrast to southern Utah where the precipitation will be focused on
an intense 12-hour period or so, central/northern Utah and southwest
Wyoming will see a prolonged period of light to moderate
precipitation for Saturday through much of Sunday. All told, valleys
could see from a 1/3rd to 3/4s of an inch of liquid with 0.5-1.5" of
SWE in the mountains (25th-75th percentile NBM accums). Current
temperature forecasts run 5-15 degrees below normal through the
weekend, with southern Utah being the furthest below normal.  There
are still some key forecast details to work out, but the bottom line
is wet and cool weather will persist through the Easter weekend with
continued additional snow in the mountains, at least maintaining if
not appreciably adding to our snowpack.

Looking ahead to next week, the aforementioned upper-level low is
expected to exit the area by Monday/Tuesday. Desert Southwest closed
lows have a habit of sticking around longer than planned (as was the
case in a recent event), however in this case it does appear that
the low will remain connected to the predominant westerlies which
will carry it away from our area. There is some uncertainty as to
how fast this occurs and how long mountain showers persist as a
result, but in all scenarios it clears out by Tuesday. A period of
ridging and quick warming follows, allowing for rebounding
temperatures and quiet conditions for the middle of next week.
Looking even farther ahead, about 80% of ensembles support yet
another cold closed low pushing into the area late in the week, this
time originating from the Pacific NW, bringing another cold front
passage and round of cool/showery weather. The other 20% show a
continued ridge with warm and quiet conditions.

&&

.AVIATION...KSLC...VFR conditions will continue throughout the
period at the KSLC terminal. Dry conditions will persist with mid
and high level clouds advecting in ahead of a cold front arriving
tomorrow afternoon. This will keeps winds southerly through the
period with gusts 20-25kt.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail
across the airspace as dry conditions with some mid and high level
clouds continue. Gusty southerly winds will precede a cold front
arriving tomorrow afternoon with showers in the high terrain
tomorrow morning before more widespread precipitation moves into
northern Utah/SW Wyoming tomorrow afternoon.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from 6 AM to 6 PM MDT Thursday for
     UTZ110.

     Winter Weather Advisory from 9 AM to 9 PM MDT Thursday for
     UTZ111-112.

     Winter Weather Advisory from noon Thursday to midnight MDT
     Thursday night for UTZ113.

     Wind Advisory from 9 AM to 6 PM MDT Thursday for UTZ115-122.

WY...None.

&&

$$

SHORT TERM...Wilson
LONG TERM...Van Cleave
AVIATION...Mahan

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity


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